Product toxicity of fine chemicals has been regarded as a serious problem that biotechnological processes face frequently. In several instances, a second phase of an organic solvent can extract the toxic product from the aqueous phase during fermentation. With the discovery of solvent-tolerant bacteria, more types of solvents may now be used in such two-liquid water-solvent systems. Toxicity of organic solvents also may be a problem in environmental biotechnology, if locally high concentrations of a solvent are present. In such instances, solvent-tolerant bacteria may be employed successfully.
A relationship has been established between the toxicity of a solvent for an organism and the partitioning of a solvent to octanol from the water phase. The logarithm of the octanol/water partition coefficient is termed log P.sub.O/W and this parameter has been taken as an indicator for the partitioning of solvents from the aqueous medium to the membrane of organisms. Generally, it is accepted solvents have their destroying effects on organisms at the level of the cytoplasmic membrane where they preferentially accumulate. As a consequence of the high solvent concentrations in this compartment, the cell is no longer able to perform essential biochemical reactions and eventually loses its integrity (see: Sikkema, J., et al., Mechanism of membrane toxicity of hydrocarbons, Microbiol. Rev., 59:201-222, 1995).
In general, organic solvents with a low log P.sub.O/W value are very toxic to microorganisms, since the compounds with low log P.sub.O/W accumulate in the biological membrane and have devastating effects on the membrane function, leading to the cell death. This hampers the development of bioconversion systems for the production of organic compounds with low log P.sub.O/W, which are toxic to microorganisms. Another problem is that many of the substrate of enzymatic reactions are rarely soluble in water and thus may not be fully bioavailable to microorganism. Naturally, as an effective way of ameliorating the organic solvent-related problems, studies have been made in search for organic solvent-tolerant organisms which can be used in the bioconversion process.
Organic solvent-tolerant bacteria are also useful in the environmental biotechnology. These microbes can be used as a vehicle for the elimination of low-molecular-weight aromatic hydrocarbons such as toluene, styrene, benzene and xylenes, which are very toxic even to the microorganisms utilizing these compounds as a carbon source. Thus organic solvent-resistant bacteria have advantages in the bioremediation of these compounds.
So far, many bacteria of Pseudomonas that are able to tolerate high concentrations of organic solvent have been discovered in the art (see: Aono, R., et al., Isolation of novel toluene-tolerant strain of Pseudomonas aeruginosa, Biosci. Biotechnol. Biochem., 1:145-146, 1992; Inoue, A., and K. Horikoshi, A Pseudomonas thrives in high concentration of toluene, Nature, 338:264-266, 1989; Inoue, A., et al., Pseudomonas putida which can grow in the presence of toluene, Appl. Environ. Microbiol., 57:1560-1562, 1991; Ramos, J. L., et al., Isolation and expansion of the catabolic potential of a Pseudomonas putida strain able to grow in the presence of high concentration of aromatic hydrocarbons, J. bacteriol., 177(14):3911-3916, 1995).